1. Field of the Invention
This invention relates to data communications and data delivery over communication media, and, more particularly, to host computer based data acquisition systems.
2. Description of the Relevant Art
IEEE 1394 is an international standard, low-cost digital interface that integrates entertainment, communication, and computing electronics into devices such as multimedia devices. Originated by Apple Computer as a desktop LAN and developed by the IEEE 1394 working group, IEEE 1394 is a hardware and software standard for transporting data at 100, 200, 400, or 800 megabits per second (Mbps). Maximum packet sizes are 512, 1024, 2048, and 4096 bytes depending on the transfer speed. 1394 provides 64-bit addressing—The 16 MSb's (most significant bits) are used for determining source/destination bus/node. As used herein, the terms “node” and “device” may be used interchangeably to denote a node on the 1394 bus.
There can be up to 1023 buses each with up to 63 nodes. The 48 LSb's (least significant bits) are used to access locations within a device's addressing space. 1394 provides for Direct Memory Access (DMA). DMA is the most powerful feature of the bus for the data acquisition purposes since it allows a device to transfer data from/into computer memory without microprocessor intervention, thus, making it very similar to the PCI bus.
IEEE 1394 also defines a digital interface—there is no need to convert digital data into analog and tolerate a loss of data integrity. 1394 is easy to use in that there is no need for terminators, device IDs, or elaborate setup. Another benefit of 1394 is that it is “hot pluggable”, meaning users can add or remove 1394 devices with the bus active. IEEE 1394 has a scaleable architecture, allowing users to mix 100, 200, 400, and 800 Mbps devices on a bus. IEEE 1394 also provides a flexible topology in that it supports daisy chaining and branching for true peer-to-peer communication between 1394 devices. In addition to asynchronous data transfer, 1394 provides isochronous data transfer, which guarantees delivery of time critical data, reducing costly buffer requirements.
Serial Bus Management provides overall configuration control of the serial bus in the form of optimizing arbitration timing, guarantee of adequate electrical power for all devices on the bus, assignment of which IEEE 1394 device is the cycle master, assignment of isochronous DMA controller ID, and notification of errors. Bus management is built upon IEEE 1212 standard register architecture. It should be noted that 1394 error notification is limited to general error detection. When an error has occurred, it may not be known when or where the error occurred, and so the delivery status of transmitted data may also be unknown.
There are two types of IEEE 1394 data transfer: asynchronous and isochronous. Asynchronous transport is the traditional computer memory-mapped, load and store interface. Data requests are sent to a specific address and an acknowledgment is returned. In addition to an architecture that scales with silicon technology, IEEE 1394 features a unique isochronous data DMA controller interface. Isochronous data DMA controllers provide guaranteed data transport at a pre-determined rate. This is especially important for time-critical multimedia data where just-in-time delivery eliminates the need for costly buffering.
Much like LANs and WANs, IEEE 1394 is defined by the high level application interfaces that use it, not a single physical implementation. Therefore as new silicon technologies allow high higher speeds, longer distances, and alternate media, IEEE 1394 will scale to enable new applications.
Perhaps most important for use as the digital interface for executer electronics is that IEEE 1394 is a peer-to-peer interface. This allows not only dubbing from one camcorder to another without a computer, but allows multiple computers to share a given camcorder without any special support in the camcorders or computers.
The IEEE 1394 bus was primarily intended for computer multimedia peripherals such as audio and video devices. One potential application for the IEEE 1394 bus is remote data acquisition and test and measurement. For example, the IEEE 1394 bus could be used to connect a remote data acquisition device or measurement device to a host computer. However, improved methods are desired for transferring data from a host computer system to a device, such as over an IEEE 1394 bus.